Unbalanced tap-changing on rectifier locomotives



May 20, 1952 J HUBBARD I 2,597,100

UNBALANCEID TAP-CHANGING ON RECTIFIER LOCOMOTIVES Filed Jan. 26, 1951 jommunicofion Szstem 32 33 \30 uence of WITNESSES: INVENTOR zfiv/ LloydJ.Hibbord.

v BY flw 4 WM ATTORN EY Patented May 20, 1952 UNBALANOED TAP-CHANGING ONRECTIFIER LOCOMOTIVES Lloyd J. Hibbard, Pittsburgh, Pa., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application January 26, 1951, Serial No. 208,062

3 Claims.

My invention relates to rectifier-powered trol- Icy-energizedequipments, and it relates more particularly to a special unbalancedtap-changing system for rectifier-power traction-motor equipments,whereby the even harmonics are balanced out in the line-currents whichflow in the trolley-wire which energizes the electricrailway vehicle ortrolley-energized coach.

My present invention is an improvement over the broad subject matterwhich is described and claimed in my application Serial No. 120,331,

,filed October 8, 1949, for Inductive-Interference Preventive-Means, inwhich a direct-current load-circuit, containing the traction-motor, andhaving a large direct-current ripple, is energized, from a single-phasetrolley which is subject to inductive interference considerations,through a rectifier-system under such conditions that there is enoughseries inductance, on the supply-circuit side of the rectifiers, toproduce a substantial angle of overlap of the half-waverectifier-currents, during each half-cycle of the supply-current. Whereis is necessary, (as is usually the case), a harmonic-reducing filter isalso provided, as described and claimed in my copending application justmentioned.

My present invention is more particularly related to a rectifier-poweredequipment of the type in which a direct-current load-means is energizedfrom the secondary winding of a power-supply transformer through tworectifiers, the returncircuit of the load-means being brought back tothe midpoint of the secondary winding. Each anode-current half-wave ofeach of the two rectifiers contains both even and odd harmonics. If thetwo anode-currents (or half-wave rectifiercurrents) of therectifier-assembly are kept equal, the even harmonics of the twohalf-waves cancel each other in the alternating-current input-circuit,while they add to each other in the directcurrent load-circuit. On theother hand, with equal anode-currents, the odd harmonics cancel eachother in the direct-current load-circuit, while they are in phase, andadd to each other, in the alternating-current supply-circuit.

In ordinary rectifier-powered direct-current load-circuits of thisnature, the anode-currents are kept equal, with the result that onlyeven harmonics appear in the direct-current load-circuit, and only oddharmonics appear in the alternating-current supply-circuit. Theseconditions have heretofore been observed in rectifier-poweredtrolley-energized vehicles, where the singlephase trolley is subject toinductive interference considerations, so that theinterference-suppressing means had to deal only with odd harmonics inthe trolley-circuit and even harmonics in the direct-currenttraction-motor circuits, as discussed in my previously mentionedapplication Serial No. 120,331.

It is an important feature of rectifier-powered trolley-energizedtraction-motors, that the speed of the direct-current traction-motorscan be very conveniently controlled by voltage-variation, obtained bysuitable tap-changing means associated with the step-down transformerwhich energizes the rectifying-equipment from the trolley. Heretofore,in order to avoid second-harmonic ripples in the trolley-circuit,thereby confounding the induction-interference problems, it has beennecessary to keep the anode-currents of each rectifier-pair balanced, sothat the second harmonics of the two half-wave anode-currents wouldneutralize each other in the trolley-current. This has necessitatedchanging the secondary-taps simultaneously, and in equal amounts, onopposite sides of the secondary midpoint, and enough secondary taps havehad to be installed, in order to obtain the necessary refinement oftraction-motor control, thus requiring more taps than would have beenrequired, if it had been possible to alternately advance the voltages,first on one side of the midpoint connection, and then on the other,during the acceleration of the traction-motors.

According to my present invention, the traction-motors of anyrectifier-powered locomotive or car, or any group of simultaneouslycontrolled locomotive-cabs or electrically-propelled cars, are dividedinto two equal groups, and the controller is so arranged that thesecondary tap-positions are advanced, first on one side of thesecondarymidpoint, and then on the other, so that each traction-motorgroup is alternately operated with unbalanced and balanced taps, withthe limitation, however, that during the unbalanced conditions, one ofthe pairs of rectifying devices is unbalanced with a larger voltage onone side of its midpoint connection, while the other pair of rectifyingdevices is similarly unbalanced with a larger voltage on the other sideof its midpoint connection. In this manner, during unbalancedconditions, the even harmonics which are produced in the line-current bythe rectifier-pair for one of the motor-groups are exactly neutralizedand cancelled out by the even harmonics which are produced in theline-current by the rectifier-pair for the other motor-group.

With the foregoing and objects in View, my invention consists in thecircuits, systems, combinations, apparatus, parts, and methods of designand operation, as hereinafter described and claimed, and illustrated inthe accompanying drawing, the single figure or" which is a muchsimplified circuit-diagram, indicating circuits and apparatus whichillustrate the general principles of my present invention, in anexemplary form of embodiment which has been chosen, out of many possibleforms of embodiment, as a basis for the explanations which are containedin the following description.

In the much simplified diagrammatic circuit of the drawing, I haveshown, by way of example, a single-phase power-supply circuit, one sideof which is connected to, and includes, a trolley wire 30, while theother side of the supply-circuit is grounded, as indicated at 31. Thetrolley wire 30 is paralleled by a communication circuit 32, such as atelephone circuit, which makes it essential to consider the inductiveinterference effects of the power-line harmonics in the telephonecircuit. The power-supply frequency may be either a previously knownrailway-electrification frequency, such as 25 cycles, or it may be ausual commercial frequency, such as 60 cycles, such as is used forcommercial power and light circuits.

In the drawing, I have diagrammatically indicated some of the essentialelectrical parts or a single locomotive or railway-car, which isenergized from the trolley wire 30 through a pantograph 33 and astep-down power-supply transformer 34 for that particular locomotive orcar. The power-transformer 34 is provided with a secondary winding 35which is used to energize the rectifier-powered traction-motor circuits.

In the illustrated example, there are four traction-motors, representedby their armatures A1, A2, A3 and A4. Each motor is provided with aseries interpole winding 3 and a series mainfield winding 37, connectedin a motor-circuit which includes a serially connected reactance orchoke coil 33, as described in my previously mentioned applicationSerial No. 120,331. It is obvious, of course, that each motor could bereplaced by a group of motors, connected either in series or inparallel, and that any even number of similar motors or similarmotor-groups could be used.

It is essential, in carrying out my present invention, that the motorsshould be divided into two equal parts, which are separately energizedthrough rectifiers. In the illustrated system, motors A1 and A2 compriseone group, which is supplied from an alternating-current supply-linecomprising the conductors LI and L2; while the motors A3 and A4 comprisethe other group, which is supplied from an alternating-currentsupplyline comprising the conductors L3 and L4. By way of illustration,one terminal of each motor, for example, the positive terminal, isenergized from the common cathode-circuit 40 of a pair of rectifiers 41and 42, each of which may be an ignitron or other single-phaserectifying device of a type which becomes substantially nonconducting,after a conducting period, only in response to a current-decrease tosubstantially zero. In other words, once a current-conducting arc isformed in either one of the rectifierdevices 4| or 42, that are willsustain itself, and will not become extinguished, until substantiallycurrent-zero.

The two rectifiers 4i and 42 of each of the rectifier-assemblies whichpowers each of the respective direct-current motors A1, A2, A: and

A4, have anode-leads 4i and 42', respectively, which are connected tothe respective conductors of the associated alternating-currentsupplycircuit Ll-L2, or L3L4, as the case may be, the motors A1 and A2being powered from the first supply-circuit LIL2, while the motors A:and A4 are powered from the other supply circuit L3-L4, as previouslyexplained. Preferably, as shown, each pair of anode-leads 4| and 42'include serially connected anode-reactor windings 4i" and 42", which arepreferably mutually coupled, on a common air-gap magnetic circuit 43, asexplained in my companion application Serial Number 210,390, filedFebruary 10, 1951, for Rectifier-Powered Equipment.

The two reactor-windings 4| and 42" of each pair are preferably coupledas closely as is practicable, as by having their respective coilsinterleaved with each other; there are the same number of turns in eachof these reactor-windings; and the polarity of the reactor-windingconnections is such that the two reactor-windings 4|" and 42" of eachpair are in seriescircuit relation to each other, producing a maximumreactance in the reactor-transformer of which they are a part, for thecommutating currents which flow between the two associated rectifyingdevices 4| and 42 during their overlapping conducting periods, all asdescribed and claimed in the companion application which has just beenmentioned.

Connected somewhere across each of the pairs of anode-leads 4l-42,either on the power-input side or on the rectifier side of theanodereactors 4l"-42", I preferably use a parallelresonant filterconsisting of a capacitor 46 and a damping resistance 41, as describedin both of my two previously mentioned copending applications. Thecapacitor is tuned in parallel resonance with the input-reactance, asseen from the filter-terminals, at some frequency in the range betweenthe third harmonic of the line-frequency and 900 cycles, for the purposeof reducing the inductive interference in the trolley-line 30.

Preferably, the supply-leads for one of the groups of traction-motors,for example the supply-leads L3 and L4, include serially connectedreactors 48 and 49 for the purpose of dephasing the line-currentharmonics which are drawn by the two groups of traction-motors,particularly the harmonics in the range which are the most obnoxiousfrom the standpoint of inductive interference, as described and claimedin my copending application Serial No. 140,475, filed J anuary 25, 1950,now Patent 2,554,248, issued May 22, 1951, for DephasedInductive-Interference Prevention. As set forth in this last-mentionedapplication, comparable harmonic-dephasing results could beaccomplished, also, by using different sizes of anode-reactors 4I"-42 inseries with different rectifier-assemblies 4l42, or by using differentsizes of filter-capacitors 46, across the anode-leads 4l'42' of thedifierent rectifier-assemblies.

The several supply-circuit conductors LI, L2, L3 and L4 are energizedfrom the midtaps of individual preventive-coils Pl, P2, P3 and P4,respectively, which are in turn energized from a tap-changing meanswhich is associated with a plurality of voltage-controlling taps TI toT. The odd-numbered voltage-controlling taps TI to TB are disposed onone side of the midpointtap X of the secondary winding 35 of thestepdown power-supplying transformer 34, while the even-numbered taps T2to TH provide corresp'onding voltages on the other side of said midpointtap X of said secondary winding 35. It will be understood, of course,that a separate secondary winding 35, or even a separate completetransformer 34, may be provided for each of the two equal groups ofmotor-loads. In the particular installation which has been selected forillustration, all of the traction-motors A1 to A4 are regarded as beingon the same car or locomotive. so that neither a plurality of secondarywindings 35, nor a plurality of transformers 34, is necessary.

The preventive-coil PI of the lead Ll of the first supply-circuit L|L2,for the first half of the total traction-motor load, is provided withtwo input-terminals PIA and PIB. The input terminal PIA is energized, bymeans of any one of a plurality of tap-switches A, C, E, G, I, K or M,from the various even-numbered voltagechanging taps T2 to T|4 on the tophalf of the secondary winding 35, the tap-switch A being connected tothe lowest-voltage tap T2. The other input-terminal PIB of thepreventive-coil PI is similarly energized, through one of a plurality oftap-switches a, c, e. y, i, k or m, from the same even-numbered taps T2to T|4, respectively.

In a similar manner, the preventive-coil P2, which is to 11 30 c. ti.the scan s ppiydeac s I2 of said first half of the motor-load, isprovided with two input-terminals PZA and PZB, which are energized fromthe odd-numbered taps Tl to Tl3, on the bottom half of thetransformersecondary 35, through the respective tap-switches B, D, F, H,J, L or N, for the input-terminal BZA, and through the respectivetap-switches b, d, f, h, 9', Z or n for the input-terminal PZB.

It will be noted that the supply-line conductor Ll, for the first groupof motors A1 and A2, is energizable with selected voltages, from theevennumbered taps T2 to TIA of the upper half of the secondary winding35, while the second supply-lead L2 of said first motor-group A1 and A2is energizable with selected voltages, from the odd-numbered taps T| toT|3 on the bottom half of the transformer-secondary 35.

Without going through all of the connections, it will suffice to saythat the two preventive-coils P3 and P4 which energize thesupply-circuit leads L3 and L4 for the second motor-group A; and A4 areenergized from corresponding tap-switches which are similar to thetap-switches which have already been described, except for the additionof distinguishing prime-marks with this difference, namely, that thetap-switches B, D, F, H, J, L and N, and the tap-switches b, f, h. :i',Z and n are associated with the respective even-numbered taps T2 to T|of the top half of the transformer-secondary 35, while the remainingprimed tap-switches are associated with the odd-numbered taps TI to T|3on the bottom half of the transformer-secondary 35.

The negative motor-terminals are connected to the midtap X of thetransformer-secondary which supplies the associated supply-line L|L2, orL3-L4, as the case may be. In the illustrated form of embodiment of myinvention, since there is only one secondary winding 35, all of thenegative motor-terminals are brought back to the same midtap-connectionX.

The starting and acceleration of the tractionmotors A1 to A4 arecontrolled by means of a controller-handle 50 which controls theposition of a multi-position controller 5|, which is diagrammaticallyindicated by means of a sequence-chart, in which the successivecontroller-positions are indicated by notches numbered from 1 to 28,(the off-position being not shown), while the various tap-switches areindicated by their respective letters. A closed position of anytap-switch is indicated by a small circle in the appropriate square ofthe sequencechart 5|. It will be noted that each primed tapswitch iscontrolled simultaneously with the correspondingly lettered switchhaving no prime.

The first notch of the controller 5| energizes the tap-switches A and A.The tap-switch A furnishes half-wave energization for therectifier-assemblies associated with the first motorgroup A1 and A2,through half of the preventivecoil Pl, from the lowest-voltage tap T2 inthe top half of the transformer-secondary 35; while the tap-switch Afurnishes half-wave energization for the rectifier-assemblies associatedwith the second motor-group A3 and A4, through half of thepreventive-coil P4. from the lowest-voltage tap TI on the bottom half ofthe transformersecondary 35. 1 Each of the two motor-groups Al-A2 andAa--A4 thus draws even harmonics from the alternating-currentsupply-line, but these even harmonics are out-of-phase with each other,because the two motor-groups are energized from different halves of thetransformer-secondary 35. Since the traction-motors are all similar, andall rotating at the same speed, the even harmonics of thesupply-circuits are equal in magnitude, and thus cancel each other out,so that no even harmonics appear in the trolley-conductor 33. or in theprimary winding of the transformer 34 (neglecting leakage).

On notch No. 2 of the controller 5|, the tapswitches B and B areenergized in addition to the tap-switches A and A, with the result thatall of the motors receive full-wave energization, in series withone-half of each of the associated preventive-coils Pl to P4, from thetwo lowestvoltage taps TI and T2 on opposite sides of the midtap X ofthe transformer-secondary 35. Since these two taps TI and T2 supplyequal voltages, 180 out of phase with each other, the two anode-currentsof each rectifier-pair are equal, so that the even harmonics balance outin each rectifier-pair, so that these even harmonics do not appear inthe trolley line 30.

The third controller-notch 3 closes the tapswitches a and a, in additionto the tap-switches A, A, B and B which were previously closed, therebycutting out the preventive-coil impedance of the preventive-coils PI andP4, leaving only two half preventive-coils P2 and P3 in circuit with therespective supply-circuits L|L2 and LS-LA of the two motor-groups, themotors still being energized full-Wave, from the lowestvoltage taps TIand T2.

The fourth controller-notch 4 closes the tapswitches b and b, inaddition to the tap-switches previously described as being closed. Theresult is to remove all of the preventive-coil impedance from thesupply-circuits L|L2 and L3L4 which energize the two motor-groups, fullwave, from the balanced lowest-voltage taps TI and T2.

Thereafter, subsequent controller-positions alternately advance thevoltages, first on one side of the midpoint connection, and then on theother, as will be evident from the sequence-chart 5|, so that therectifier-assemblies are alternately balanced and unbalanced, receivingsuccessively higher voltages, in such manner that the unbalancedconnections are such that the pairs of rectifying devices ll-42 for onemotor-group A1 and A2 are unbalanced with a larger voltage on one sideof their midpoint connection X, while the pairs of rectifying devices4l-42 for the other motor-group A3 and A4 are unbalanced with a largervoltage on the other side of their midpoint connection X, thus balancingout the supply-circuit second harmonics, so that they do not appear inthe trolley-wire 30.

Experience has shown that the direct-current traction-motors A1 to A4are well able to withstand the additional harmonics which are producedin the various motor-circuits by the abovedescribed unbalancing, withoutdiscoverable additional heating, and while still maintaining black orperfect commutation. My use or alternate unbalanced tap-connections,followed by balanced tap-connections, materially reduces the number oftaps T! to T14 which have to be brought out from the secondary winding35, thereby reducing the cost and the complication of the equipment, andalso making it possible to operate the rectifier-s 4i and 42 of thevarious rectifier-assemblies without resorting to the expedients ofdelayed firing, or of excessive voltage-regulation, for the purpose ofreducing the necessary number of taps.

While I have described only a single extremely simplified andillustrative or exemplifying form of my invention, designed to beindicative rather of the general principles of my invention than showingprecise details of the actual complicated connections such as would beused in practice, I wish it to be understood that my invention is notlimited to the illustrated form or circuit. I desire, therefore, thatthe appended claims shall be accorded the broadest constructionconsistent with their language.

I claim as my invention:

1. Rectifier-powered equipment, comprising, in combination, two similardirect-current loadmeans; a single-phase supply-circuit;transformer-means energized from said single-phase supply-circuit andhaving a plurality of secondary taps including a midpoint tap and arality of similar voltage-controlling taps on opposite sides of saidmidpoint tap; a separate rectifier-assembly for each of thedirect-current load-means, each rectifier-assembly comprising a pair ofsingle-phase rectifying devices; means for connecting one terminal ofeach directcurrent load-means to a secondary midpoint tap; means forconnecting the other terminal of each direct-current load-means tolike-polarity terminals of the associated pair of rectifying devices; atap-switching means associated with each of the voltage-controllingsecondary taps; and controlling-means for energizing each of theother-polarity terminals of each pair of rectifying devices throughselected tap-switching means on opposite sides of the midpointconnection of the associated load-means; characterized by saidcontrolling means, at times, providing unbalanced voltages to saidother-polarity termi nals of each .pair of rectifying devices, in suchmanner that one of said pairs of rectifying devices is unbalanced with alarger voltage on one side of its mid-point connection, while the otherpair of rectifying devices is similarly unbalanced with a larger voltageon the other side of its midpoint connection.

2. The invention as defined in claim 1, characterized by saidcontrolling-means, at other times, providing only a half-waveoperatingvoltage for each of the rectifier-assemblies, with thehalf-wave secondary tap of one rectifierassembly on one side of itsmidpoint connection, and with the half-wave secondary tap of the otherrectifier-assembly on the other side of its midpoint connection.

3. The invention as defined in claim 1, characterized by saidcontrolling-means having a plurality of controller-positions and beingoperative to provide progressively higher directcurrent voltages forsaid load-means, in successive controller-positions; the firstcontrollerposition providing only a half-wave operatingvoltage for eachof the rectifier-assemblies, the half-Wave secondary tap of onerectifier-assembly being the lowest-voltage tap on one side of themidpoint connection of the associated loadmeans, and the half-wavesecondary tap of the other rectifier-assembly being the lowest-voltagetap on the other side of the mid-point connection of the associatedload-means; a subsequent controller-position providing balancedfull-wave operation of both rectifier-assemblies, with each of therectifying devices energized from the lowest-voltage tap on itsappropriate side of the midpoint connection; and subsequentcontrollerpositions alternately advancing the voltages, first on oneside of the midpoint connection and then on the other, so that therectifier-assemblies are alternately unbalanced and balanced, theunbalanced connections being as described in claim 1.

LLOYD J. HIBBARD.

No references cited.

